1. Field of the Invention
The invention relates to a method of titanium nitride film deposition and, more particularly, to a method of forming a thick, low stress titanium nitride film having low resistivity.
2. Description of the Background Art
In the manufacture of integrated circuits, a titanium nitride film is often used as a metal barrier layer to inhibit the diffusion of metals into an underlying region beneath the barrier layer. These underlying regions include transistor gates, capacitor dielectric, semiconductor substrates, metal lines, and many other structures that appear in integrated circuits.
A combination of titanium/titanium nitride (Ti/TiN) is often used as a diffusion barrier and provides contacts to the source and drain of a transistor. In forming a contact using a tungsten (W) plug process, for example, a Ti layer is deposited upon a silicon (Si) substrate, followed by conversion of the Ti layer into titanium silicide (TiSix), which provides a lower resistance contact with Si. A TiN layer is then formed upon the TiSix layer, prior to forming the tungsten plug. Alternatively, in some applications, a TiN plug may also be formed instead of a W plug.
Ti and TiN films can be formed by physical or chemical vapor deposition. A Ti/TiN combination layer may be formed in a multiple chamber xe2x80x9ccluster toolxe2x80x9d by depositing a Ti film in one chamber followed by TiN film deposition in another chamber. When depositing both Ti and TiN using chemical vapor deposition (CVD), titanium tetrachloride (TiCl4), for example, may be used to form both Ti and TiN films when allowed to react with different reactant gases, i.e., under plasma conditions, Ti is formed when TiCl4 reacts with H2, and TiN is formed when TiCl4 reacts with nitrogen. In general, TiN can be formed by reacting TiCl4 with a nitrogen-containing compound under either plasma or thermal conditions, depending on the specific nitrogen-containing compound. Thus, a TiN film may be formed by high temperature CVD using a reaction between TiCl4 and ammonia (NH3). However, thicker TiN films deposited using some prior art processes tend to develop cracks, especially when the film thickness exceeds about 400 xc3x85. With increasing film thickness, both the density and size of the cracks increase, until the film eventually peels off.
Furthermore, when a TiN film is deposited from a TiCl4-based chemical process, chlorine (Cl) is entrained in the TiN layer. The Cl content has been associated with an increase in film resistivity, which in turn results in an undesirable increase in contact resistance. For TiN plug applications, a TiN film thickness of over 1000 xc3x85 is often required, and a reduction of film resistivity becomes even more important.
Although the Cl content in the deposited TiN film can be reduced by increasing the deposition temperature, improved step coverage is favored by lowering the deposition temperature. Furthermore, a relatively low deposition temperature is advantageous for process integration purposes. For example, TiN can be used as a barrier layer for an upper electrode in a capacitor structure with tantalum pentoxide (Ta2O5) as the dielectric. However, thermal CVD of TiNxe2x80x94e.g., using a reaction between TiCl4 and NH3, is often performed at a temperature of about 650xc2x0 C. Such a high temperature may cause undesirable atomic inter-diffusion within the capacitor structure.
Therefore, a need exists in the art for a method of depositing TiN at a reduced temperature, to yield thick, crack-free TiN films having improved properties including good step coverage and low resistivity.
The present invention is a method of forming a titanium nitride (TiN) layer using a reaction between ammonia (NH3) and titanium tetrachloride (TiCl4) at a pressure of about 10 to about 50 torr and a temperature of less than about 600xc2x0 C., followed by treating the TiN layer in a hydrogen-containing plasma.
In one embodiment of the present invention, the TiN layer is formed at a pressure of about 20 torr and a temperature between about 550xc2x0 C. and about 600xc2x0 C. at an NH3:TiCl4 flow ratio of about 8.5, followed by in situ plasma treatment in the presence of H2. Under these process conditions, a TiN layer of at least 250 xc3x85 can be formed. By repeating the TiN deposition and plasma treatment for additional cycles, a composite TiN layer of desired thickness can be formed for plug-fill applications. The method of the present invention can also be used to form a TiN layer as part of an upper electrode in a capacitor structure. The treatment of the TiN layer may be performed using a radio-frequency (RF) local plasma or a remote plasma.
In an alternative embodiment, alternate TiN layers can be formed using different deposition conditions. For example, a second TiN layer having step coverage and/or stress characteristics different from the first TiN layer may be formed by using an NH3:TiCl4 flow ratio that is different from that used in the first TiN layer. By alternating between deposition and treatment of the first and second TiN layers using different processing conditions, a composite TiN layer of final desired thickness can be achieved, with improved overall step coverage and stress characteristics.